Abstract
Rapid manufacturing using laser beam and/or electron beam has been applied to fabrication of artificial hip and knee joints in quite recent years. In the electron beam melting (EBM) method, the high energy electron beam effectively melts the metal powder without creating flaws such as porosities or inclusions of oxide particles during building. Thus it is found that EBM technique for rapid manufacturing of artificial hip and knee joints processes a higher possibility as the next-generation methodology for fabrication of the medical devices such as hip and knee joints. In the present study, we focus on the EBM technique. The microstructures and mechanical properties of Co-29Cr-6Mo alloy with C and N additions, produced by using EBM method, were studied using X-ray diffraction, electron back scatter diffraction, transmission electron microscope (TEM), Vickers hardness tests, and tensile tests, focusing on the influences on the build direction and the various heat treatments after build. It is found that the microstructures for the as built specimens were changed from columnar (Fig. 1a) to eqiaxed grain structure (Fig. 1c) with average grain size of approximately 10–20 μm due to the heat treatment employing the reverse transformation from a lamellar (hcp + Cr2N) phase to an fcc phase. Our results will contribute to the development of biomedical Ni-free Co–Cr–Mo–N-C alloys, produced by EBM method, with refined grain size and good mechanical properties, without requiring any hot workings.
Fig. 1 Inverse pole figure (IPF) maps of microstructure of samples produced by EBM method, taken by EBSD. (a) as-built, (b) after aging treatment, (c) after reverse transformation heat treatment (RT-HT).
